YENAGOA, Nigeria (Reuters) - Vandals attacked a crude pipeline belonging to Nigeria's state oil firm NNPC in the restive Niger Delta, a military spokesman said on Friday.

"It was sabotage by vandals," military spokesman Thomas Otuji said, when asked about a claim by a militant group called Niger Delta Greenland Justice Mandate of an attack of the NNPC pipeline near Iwhremaro on Thursday night.

The group, which has claimed previous attacks, said in a statement it had carried out the attack at about 9pm on Thursday and warned

"Now you shall know what uprooting of your cherished assets means," it said to the government and major oil companies that work in joint ventures with NNPC. "More to come in the coming days."

There was no immediate information on the impact on Nigeria's oil production. The attacks have reduced output by 700,000 barrels per day, around a third of its production, since the start of the year.

Militants say they want a greater share of Nigeria's oil wealth to go to the impoverished Delta region. Crude sales make up about 70 percent of national income and the vast majority of that oil comes from the southern swampland.

Nigeria, an OPEC member, was Africa's top oil producer until the recent spate of attacks pushed it behind Angola.

President Muhammadu Buhari has said the government is trying to negotiate a lasting solution with the militants but there has been no visible progress. The militant scene is splintered into small groups, made up of mostly of unemployed men, which even their leaders struggle to control.